When nonvolatile read only memories have been programmed, the data stored in the memory are checked. To this end, the data are read again using more stringent criteria than during a later, normal read operation. As an example of this, mention will be made of the read operation in a memory in which the current in a memory cell which is being read in the memory is compared with a reference current. A different reference current is used for a check.
Test reading involves the contents of the individual memory cells in the memory array being read and being compared with a reference current which corresponds to one state for a memory cell. The comparison with the reference current provides a logic weighting. In a second read operation, all of the cells in the memory array are read again and are compared with a reference current which corresponds to the other logic state for a memory cell. A method for test reading stored logic states in a memory device produces a test signal which is dependent on the nominal value of the logic state. This test signal is compared with the logic state which is under test. Since a test signal is always produced for each logic state which is under test, said test signal being used to assess whether the state under test is correct, one read operation for all of the memory device's states under test is sufficient. It goes without saying that each logic state under test for the memory device is stored in a memory cell in the memory device.
During such implementation, the data in the memory are read twice. This results in an increased test time, which has disadvantageous effects on the total production time and hence the costs, particularly during mass production, for example in chip cards.